The invention relates to a circuit arrangement for rotation speed regulation of a hydrostatic machine connected to a conduit with impressed pressure.
In the known electrical speed regulation of such a machine (German Patentschrift No. 3441185, Aug. 13, 1987) the rotation speed desired value and the rotation speed actual value generated in a tachogenerator or other pickup are supplied to the rotation speed regulator. Connected to the speed regulator is a pivot angle adjustment means for the machine. The pivot angle of the machine working as motor for driving a load defines the absorption (displacement) volume. This generates a torque for driving the load, a corresponding speed of rotation resulting.
With very small adsorption (displacement) volumes of the machine corresponding to relatively small rotation speeds of regulation behavior of the machine is greatly impaired because in the region of very small speeds there is no proportionality between the pivot angle of the machine and the torque generated by the machine. There are several reasons for this: with reciprocating piston machines during a revolution the number of acting operating pistons changes, this also changing the torque generated. Furthermore, the frictional torque arising at the machine and the leakage losses depend on the rotation angle so that this also reduces the uniformity of the torque.
The consequence is that at small rotation speeds the drive turns jerkily and irregularly and can even stop altogether under load. Under such operating conditions the control operation carried out by the speed regulator takes place too late and as a result due to the phase displacement between rotation speed deviation and correction no uniform speed can be set.
The problem underlying the invention resides in improving the circuit arrangement for the rotation speed regulation of the type outlined at the beginning so that even very small speeds can be reliably controlled.